Manufacture of rubber



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Patented May 24, 1938 MANUFACTURE or RUBBER.

Roscoe H. Gerke, Nutley, George H. Ganzhorn,

West Englewood, and Louis H. Howland, Nutley, N. J., and Hugh M.Smallwood, New York, N. Y., assignors to United States Rubber Products,Inc., New York, N. Y., a corporation of Delaware Application September14, 1935, Serial No. 40,534

20 Claims. (Gl. 10B-23) mixes prior to vulcanization thereof, whereby toUsual product Improved product confer upon the rubber composition adesired sum a total of physical and chemical properties. High resistanceto ab- Higher resistance to `Investigators of the behavior oi.' carbonblack msm abrasion in rubber have long sought 'to effect improve- HardRelatively softer ments in the physical properties of rubber-and-V mghmodulus Relatively lower modu' carbon black compositions throughimproving the Ixus at 10:1 ongation 1o degree of dispersion of thecarbon meek. They Reunvelyb g er ggd" 1o have round that the evidencepeints to the exelggatorl istence of a poorer degree of dispersion oithe High hysteresis 'Low hysteresis .A

carbon black in the vulcanized compositionthan W l tn l i ti Hi h l tril sis in the unvulcanized composition. It is likewise it cec ca' M ss vivite ec ca re 16 agreed that this is due to extensive tlocculation -y yl5 of the carbon black during vulcanization. Ei'- Hardness values oftire treads containing 40 forts to prevent this flocculation duringvulcanito 50% by weight of carbon black based on the nation and hence toimprove the dispersion of rubber, according to the Adams densimeter,range the black in the vulcanized rubber have refrom about 40 to about50 or higher ior the 20 peatedly met with failure. It has been predicted4improved products and from less than 25 to 20 for many years that theeventual discovery of about 35 for the products produced by theconmethods for obtaining better dispersion of carventional and ordinarymethods. By increasing bon black in vulcanized rubber would result inthe carbon black ratio up to from 60 to '10%, the production of softercured stocks having the hardness of the new product may be' broughthigher resistance to abrasion and inthe use of Within the range ofhardness of ordinary stocks. 25 tire treads having higher concentrationsof car- Such high amounts of carbon black cannot be bon black.successfully used in the ordinary methods of 'I'hese objects have nowbeen accomplished by processing tread stocks but by this invention, adiscovery which is embodied in the present such high amounts of carbonblack can be sucinvention, by which it is now possible to producecessfully used when they are desired. 30 tires, the tread portion ofwhich shows an imi The modulus of the improved products ranges provementin resistance to abrasion of 30%.or from 10 to 35 percent lower thanthat of simimore compared to the treads of tires which have lar productsprepared by the usual methods, at heretofore been known .to have themost resistelongations of less than about 200%, At elongaance toabrasion, for example those of U. S. P. tions above about 300% andup tothe point Voi? 35 No. 1,984,247. There are also important imrupture, themodulus of the new product is higher provements in various otherdesirable characterthan that of the old product. The ultimate elonisticsof the products. In the determination of gation of the new product isgenerally somewhat these improvements in properties, various qualilowerthan that of the ordinary product, so that tative and quantitativemethods were used to arthe tensile strength at rupture is usuallyslight- 40 rive at a comparison of products produced by ly lower by anamount usually not exceeding the conventional methods with productsproduced about 10% of the tensile strength of the correaccording to thepresent invention. The results sponding product produced by conventionalof these various tests show the following conmethods. l

The torsional hysteresis values of the new prod- 45 Y. This inventionrelatesv to improvements in the technique of processing highcarbonrblack-rubber trusting and differentiating characteristics betweenthe usual product and the improved product.

ucts range from about 0.035 to about 0.08 at 280 F., whereas the valuesof similar compounds, conventionally prepared, range from 0.12 to 0.25and rarely as low as 0.10.

For vulcanizates containing 40 to 60- parts of carbon black per 100parts of rubber, the new ,tively isolated from each other.

products show a specific electrical resistivity of at least 1011ohm-centimeters and usually of at least 1012 ohm-centimeters, whereasconventional products range from less than 10 to about 10ohm-centimeters, according to the type or brand of carbon blackemployed.

The new and useful properties of the conipositions of the presentinvention areascribed to the hereindisclosed method of heating andmilling a rubber-carbon black mix under conditions whereby the carbonblack is rst severely flocculated and is thereafter deilocculated andrendered substantially particulately dispersed in the rubber, whichstate of dispersion is not materially disturbed by the subsequentvulcanizing operation. This condition of particulate dispersion does notrefer to uniformityof distribution in the rubber nor to the absence ofmacroscopic lumps of unmixed carbon black, which are ,conditionsobtainable by known methods of mixing and sometimes, for lack of abetter term, called is dispersed, at least to a large extent,`in theform of discrete particles of a size approaching or approximating thesize of the ultimate parti-- cles, in which condition the yparticles areeffec- The actuality of this condition of the carbon black particles inthe vulcanized rubber products of the invention follows from theextremely high electrical resistivity of the products, indicating thatthe carbon particles, which intrinsically are conductors of electricity,are electrically insulated from one another, and it follows also fromthe low hysteresis characteristics of the products, indicatingcomparative freedom from agglomerated carbon black particles infrictional contact with one another.

In contrast, the condition in ordinary high carv bon black-rubbervulcanizates is that the carbon' black is known to be present to a largeextent in the form of agglomerates, each of which is made up of manymutually cohering particles, and/or in a fiocculated state forming anet-work structure of filler particles having particle-tothermore, suchstructures provide continuous,

paths of relatively low resistivity for the conduction of electricitythrough the rubber. This socalled ilocculation of carbon black is knownto be induced by heat and the tendency to flocculate .is more pronouncedthe ner the particle size of the carbon black. Tests of conventionallyprepared vulcanizates, using for comparison various blacks ranging inaverage size from about 1 micron, which is characteristic of therelatively coarse, non-reinforcing or "soft vrubber blacks. down tovalues on the order of 0.01 micron or less which are characteristic ofultra-fine paint blacks and ink blacks, showed increases in the hard-`Non-conventional ness, the electrical conductivity and-thetorsionalhysteresis in the order of increasing neness of the blacks, theseconditions being indicative of increased o'cculation in the same order.

More particularly, the new vulcanizates result from incorporating in therubber a relatively large amount of carbon black, for example, atleast25 parts, and preferably at least 40 parts in the case of the tiretreads, by weight of carbon black per parts by weight of rubber, andthen subjecting a homogeneous mixture of the ingredients to a heattreatment at a temperature substantially above 250 F., the preferredtemperatures being in the range from about 300 F. to about 370 F. andmasticating the mix during and/or after such heat treatment, oralternately therewith. The duration of the special heat treatment mayvary withthe temperature employed, the higher the temperature theshorter the time, and is governed also by the degree of change desiredin the enumerated properties of the ultimate vulcanized.

. found suitable for most purposes and particularly within the preferredtemperature range. In

vpractice it is diillcult to maintain a uniform temperature throughoutthe batch and throughout the duration of the heat treatment becauseduring milling the temperatures tend to 'rise by from 10 to 50, theextent of the rise in temperature depending upon the duration of themilling, the

efliciency of the cooling system, the sizeof the batch and otherfactors, but such rise in temperature is found to be beneficial so longas the temperature does not become too high. It .is to be understood ofcourse that the heat treatment is to be controlled within limitsavoiding serious degradation of the rubber.

It has been observed that as the duration of the heat treatment at agiven temperature is increased, the electrical resistivity and thehysteresis characteristics of the ultimate vulcanized products approachthose of pure gum stocks, the resistance to abrasion goes through apronounced maximum, and the modulus at elongations above 300% increaseswhile the ultimate elongation, tensile strength and hardness undergo agradual decrease.

The succession of fundamental processing steps of the method of thepresent invention may be represented as follows: i

Conventional Y bon black 3. Hot milling or heater treatment preferablyfrom about 300 to about 370 F. plus hot or cool milling to recovery oi'plastic properties 4. Completing incorporation of vulcanizng and otherdesired ingredients prior to shaping and vulcanization Moreparticularly, with reference to the combination of masticating and heattreatment steps, these may be carried out concurrently, or the two stepsmay be carried out successively, or in alternation one or more times;for example, the heat treatment and the mastication may be effectedconcurrently by milling a pre-mixed homogeneous batch comprising carbonblack and rubber on a very hot mill of either the external or the in-Conventional dered considerably harder, and rough and dull v inappearance. The recovery of the batch to the desired smooth plasticconsistency will in somel cases be accomplished during the continuationof the hot milling, and in other cases will require a further milling atlower temperatures. The hot milling is therefore best `followed by afurther milling on a relatively cool mill, that is, at ordinary millingtemperatures, say between 100 and 200 F., for a few minutes or longer,preferably before the recipe is completed by the addition of theremainingdesired ingredients. Alternatively, the heat treatment and themastication may be effected successively by exposing a homogeneousmixture comprising carbon black and .rubber to the required hightemperature in a suitable heater, such asan oven, tank, or curing boxcontaining 'a suitable heating fluid such yas water, air, steam,nitrogen or the like, and subsequently, or in alternation with such heattreatment, milling the mixture for a short time.

The visible changes taking place during the special treatment areherewith to be described with reference to the hot-milling method. Themixture comprising rubber and carbon black, when well prepared by theusual methods, has a smooth, glossy, and homogeneous appearance,especially at a freshly cut surface, and has a viscosity such that itmay easily be worked on the mill. After this mixture is transferred toanother mill which has been pre-heated to 300 F., and worked, thesurface of the batch becomes dull, `dry and rough, the viscosityincreases very markedly, and in the case of a roll mill the batchusuallyl tends to lift from the rolls and to run through the nip withoutow or without forming a bank.V Then, as the hot-milling is continued,the batch begins to smooth out and become more plastic; finally, by theend of the hot milling period or during the subsequent milling at alower temperature, the batch recovers its former glossy, homogeneousappearance, smooth milling qualities, softness, and normal viscosity. Itwill be noted, however, that the early stage and the later stage of thehot millingperiod are not necessarily sharply distinguished with respectto time, but may overlap, the changes characteristic of each stagesometimes tending to proceed simultaneously to a certain extent.

Parallelihg these visible changes are very large changes in theelectrical resistivity of the batch. The batch as initially prepared hasa certain specific resistivity which depends principally upon the amountand type of carbon black employed and is found to be on the order of109' to l0u ohm-centimeters for the proportions and types of blackcommonly used in tire treads. The stiffening which occurs ai'ter thebatch is 'put on the hot mill is accompanied by a very large.

decrease in the resistivity, which falls to a value on the order of 10ohmcentimeters or less. Then, as the hot-milling continues and the batchbecomes more and more plastic, the resistivity increases progressivelyand finally reaches a value greater than 1012 ohm-centimeters, forexample a value on the order of 1014 or 10l5 ohmcentimeters.

In the heater method the changes which take place while the batch is intheheater are similar torand correspond to the initial changes whichoccuril` on the hot mill in the hot-milling method;

and, likewise, the milling following'the heater treatment effectschanges similar to those which characterize the recovery period in thehotmilling method.

The differences in the course of the conductivity changes during theprocessing of rubbercarbon black mixtures according to the invention andaccording to conventional procedure, respectively, are showndiagrammatically in the drawing. The specific electrical resistivity inohm-centimeters is represented by a logarithmic scale on the verticalaxis, and time on the horizontal axis without a definite scale. Thedotted curve OA corresponds to the conventional mixing of the rubber andcarbon black master batch (2:1), at the end of which the resistivity, asstated above, depends principally on the type of carbon black employed.Curve ABC is for the conventional procedure of mixing and curing; theportion AB shows the negligible increase in resistivity incident to theadmixture of the further ingredients required to make the stockvulcanizable, and BC shows the fall in the resistivity to asubstantially constant value during vulcanization, the resulting lowresistivity being due to flocculation of the carbon black duringvulcanization. Curve ADEFG is for the process of the present invention,the heating and milling being represented separately for convenience: ADshows the very rapid fall in resistivity, corresponding to a severeilocculation of the carbon black, which is effected by heating at hightemperatures; DE shows the tremendous increase in resistivity,corresponding to the defiocculation and ultimate dispersion of thecarbon black, during the recovery period of milling, a value closelyapproaching that of a pure gum stock being attained; and EF and FG,respectively, show the absence of any material change in the resistivityduring admixture of the remaining ingredients and during vulcanization,corresponding to the retention of the non-ilocculated particulatecondition of the carbon black in the vulcanized rubber.

The choice of different types of carbon black results in resistivitycurves essentially similar in shape to those of the drawing, the variouspoints only being shifted more or less, vertically, according todifferences in the flneness of the various carbon blacks.

Corresponding to the decrease in electrical conductivity of the batchduring the hot milling (after the initial stage of high conductivity ispassed) there is also a progressive change in the torsional hysteresisof vulcanized portions `prepared from samples taken from the batch atsuccessive intervals during the hot-milling, the hysteresis becominglower and lower and finally reaching a value approximating or equallingthat of a pure gum compound or of a compound loaded only with inertfiller.

In the conventional process of mixing and milling carbon black-rubberbatches to a smooth, homogeneous condition, the mill rolls are generallycarefully maintained at relatively low temperatures, the cooling of thebatches often being aided, so as to prevent scorching, by the additionof oils and similar softening agents and by cooling the mill whennecessary. It will therefore be apparent that the high temperaturetreatment and recovery of the homogeneous batch comprising carbon blackand rubber of the present invention,.is a novel treatment which issupplementary to and distinct from the steps commonly practiced in theproduction of high carbon blackor possibly an interaction between therub rubber products, particularly abrasion resisting products such astreads for tires.

The real nature or mechanism of the interaction between the rubber andthe carbon black is not fully understood but tests show that heatlng ofthe rubber alone prior to admixture with the black is ineffective toproduce the results oi.' the invention. Neither are. the results of theinvention brought about by the heating incident to the vulcanization athigh temperatures of conventionally prepared rubber compositionscontaining carbon black, because the occulation of the carbon blackwhich is effected by such heating is rendered ilxed and irreversible bythe vulcanization of the rubber and the consequent loss of its plasticproperties. This explains the relatively high conductivity, hysteresisand hardness of the ordinary highly loaded carbon black vulcanizates. y

0n the contrary, in the present process, the severe flocculationattending the high temperature treatment'is a reversible condition whichis dissipated when the mixture is again madev smoothly plastic bymilling at high and/orAow' temperatures for a suitable length of time.Another view which may be taken is that the high temperature treatmenthas apparently eii'ected a. change in the rubber and/or the carbon blackr and the carbon black, by virtue of which the carbon black is capableof being completely wetted by the rubber. Continued milling ofthefmixture during or after the high temperature treatment, then,results in the disintegration of carbon black aggregates intoexceedingly fine particles and in the substantial elimination ofparticle-'to-particle contacts, as evidenced by low hysteresis and lowconductivity. Thus it is considered th t this subsequent milling-hasbroken up the cv rbon black aggregates into ultimate particles whichhave become dispersed throughout the rubber and are individuallysurrounded by rubber. Flocculation of the carbon black is nowpractically impossible, or at least is so retarded that the state ofsubstantially complete discontinuity and dispersion of the carbon blackphase is maintained throughout subsequent operations includingvulcanization, and is preserved in the resulting vulcanizates.

Because the physical elements or units involved are below the .limits ofresolution of the microscope, microscopic methods cannot be used tofollow the actual state of dispersion of the carbon black in the variousstages. However, the low torsional hysteresis values and the highelectrical i esistivity values provide evidence of the state ofunocculated particulate dispersion of 'the black in the vulcanizates oithe invention.

The invention is further speciiically illustrated with respect to theprocessing vof tire tread compositions, it being understood that suchcompositions before they are vulcanized are to be subjected to the usualsteps of shaping, manipulation and mounting attendant the manufacture ofa vehicle tire, whether of the solid or` pneumatic -v variety, and inwhich the iinal article embodies at least as its tread portion, thevulcanized composition of the invention. l

Example 1.-Hot milling method:

A carbon black master batch comprising 100 parts of smoked sheets and 45parts oi' Cabot carbon black (by weight) was mixed in the conventionalmanner. Part of this master batchv was then used to prepare twodifferent vulcanizable stocks according to vconventional procedure,

by admixing therewith vulcanizing and other ingredients in suitableproportions, using two din'erent accelerators for the two stocks.Another part of the black master batch was placed on a roll mill whichhad been pre-heated to about 300 F., and was milled for 30 minutes,during which the temperature of the rubber rose to about 340 F.Thereafter the batch was allowed to cool, and was then milled for 2 to3minutes at a roll temperature of about 100 F. until it reached aviscosity suitable for further compounding. This heat-treated masterbatch was then used to prepare two corresponding vulcanzable stocks bycompounding in the same way as for the untreated master batch. Thevulcanization accelerators used were typical of those widely used intire treads. The complete recipes (parts are by weight) were:

The four resulting stocks were then cured in molds, at appropriatetemperatures for the respective accelerators employed, the A stocks Yminutes at 275 F., and the B stocks 90 minutes at 293 F. The physicalproperties of the resulting vulcanizates are 'compared in the followingtable (in which Conv. and "H. T. M. indicate stocks prepared from theconventional and from the high-temperature-milled master batches,respectively):

(Thiazole accela- (Aldehyde-amine rator) accelerator) Conv. H. T. M.Conv. H. T. M.

Log. R 8.8 12 8.0 12 'Torsional hysteresis (280 F.) 0. 126 0. 044 0. 1170. 063

Abrasion resistance (low speed) 100 136 100 126 Abrasion resistance(high 100 133 100 124 Hardness (Adams densimeter) 39 49 36 47 Tensilestrength (lha/sq. in.)- 4387 4100 4050 3655 Ultimate elongation, 620 510570 510 Permanent set (inches per inch) 0.35 0. 22 0. 31 0. 3l 100% 287214 327 215 Modulus (lbs.lsq.in.) 200% 771 696 725 649 at elongationoi`. 300% 1457 1668 1357 1525 400% 2350 2953 2222 2430 m09.; 3413 39233355 3437 Example 2,-High temperature heater treatment:

Carbon black and smoked sheets were mixed in the usual manner on a36-inch roll mill and sheeted out to a thickness of 1/4 to inch. Oneslab being retained as a control, the rest were heated in an atmosphereof steam for various lengths of time at temperatures of 316 and 338 F.(158 and 170 CJ. The heated slabs were found to be ,hardand of lowresistivity. They were then plasticized by running on a cool mill for 2or 3 minutes, whereupon the resistivity was found to have increased by afactor of one hundred or more. Vulcanizlng and other ingredients werethen added to each batch, including the unheated control, in thefollowing proportions per 100 parts of rubber by weightgButyraldehyde-metlrvlene anlline condensate 0.75

Buli'ur 4 Press cures of each 4riiix were Vmade at 293 F.

Mooney plastometer (Ind. and Eng. Chem. Anal. ed. vol. 6, p. 147, March1934) resistivity measurements were made on the recovered batches,

" as for the thiazole stock in Example l, and were cured at 274 F.Physical tests on the raw and the vulcanized specimens are summarized inthe following table.

Conven- H. T. M tional Time oi high-temp. milling (minutes) 30 60 w imTemp. of bank (F.) B25-355 340-355 345-358 338-355 Plasticity (Mooney):

Before recovery (129. 113. 5 54. 5 44 40. 0 Aiter recovery..."v 59.543.0 38 35. 5

Log R o1 recovered batch:

Before further heetmg.- 8. 8 l2 12 12 12 After 30 min. heating 7. 2 l212 12 12 Minuta Vulcanzam cure 30 7. 1 Log R 12 12 12 l2 30 .149 076 067.057 .067 Torsional hysteresis at 280 F 60 140 .063 .051 .049 049 90 141061 0% 046 047 30 100 144 on soft to best)- Abrasion resistance (lowspeed) 60 100 121 129 136 114 Q0 lll) 119 132 122 114 30 37 56 63 68 5BHardness (Adams) 60 4 28 44 50 54 54 90 26 40 44 48 40 30 4112 335 22131883 m00 Tensile strength (Iba/sq. in.) 60 4915 3727 2930 2788 2387 904475 3006 3mi 2988 2636 30 660 5m 450 440 440 Ultimate elongation, 00060 510 4m 42) 390 90 Bw 5m 430 390 390 The physical properties of thevulcanizates are compared in the following table, as well as theresistivity of the high-temperature heated samples otunvulcanized masterbatch before and after re-milling.

It is seen that with increased time of hotmilling, the resistivityquickly reaches a value above 1012 ohm-centimeters, the torsionalhysteresis approaches asymptotically a minimum value close to that 'of apure-gum compound, and

Temp. 011100011; Nom 310 F. (153 c.) 338 r. (110 c.) (conven- 'rims111mm (min.) mm1) 13 30 43 00' 11s 30 a0 oiresistivity; cated masterbatch 9. 0

m 0.9 0.3 0.7 0. es 0.1 0.a 12.0 11.1 11.3 12.0 120 11.0 11.0 n.3 10.011.3 12. 10.0 11.4 12.0

Inwspeeu-mt 100 113 121 110 110 112 112 11s H hmmm: 100 100 101 113 113110 113 113 (110mg) 31 41 40 h 42 40 43 44 44 Tonio n .130 .070 .012.ooe .072 .012 .00s Tm1M1bs./sq.1n.)-. 4043 3030 3003 3m 3500Elongntion, ultimate 620 500 020 co0 57o It is seen that the resultsobtained by the the tensile strength, lultimate elongation, and

'in the conventional way. Diiierent portions of this batch werehot-milled for periods of 30,

60, 90 and 120 minutes at temperatures above 300 F., and were thensmoothed out or recovered by a short milling on a cool mill. Plasticitywas measured before and after this recovery, by the actual hardnessdecrease progressively, while the abrasion resistance goes through amaximum at one hours heating.

Example 4.--Effect of increased amounts of carbon black:

Three master batches were prepared in the conventional manner containing45, 55 and 65 parts of carbon black (by weight), respectively, per 100parts of rubber. One half oi' each master batch was then subjected tohigh-temperature milling for 30 minutes, the temperature of the millrolls at the beginning oi' the period being Abrasion resistance (lowspeed) 4% between 300 and about 325 F.. and the temperature oi.' thebatches reaching `350 to 370 F., byl the end of the period. The sixbatches (three treated, three untreated) were then compounded byadmixture of the following ingredients (parts per 100 parts of rubber,by weight) Cures were made at 293 F. The'properties of the raw and curedstocks are as follows:

'I'he abrasion resistances of the conventional samples in the aboveExamples 1-5 ,is assigned a value oi 100, values higher than 100denoting correspondingly higher abrasion resistance.

Electrical resistivity was determined by measuring the resistance of aspecimen of known thickness (about 0.1 inch) placed between mercuryelectrodes, under a potential Vdiil'erence of 135 volts, using asensitive galvanometer with an Ayrton shunt.

The torsional hysteresis (Kzw'r.) represents the logarithmic decrement(base l) of the observed amplitudes of successive oscillations of atorsion pendulum, measured at k280 F. (137.8 C.) with an apparatusconsisting essentially of a torsion pendulum in which the sample ofrubber tested supplies the restoring force whent Treatment ConventionalH. T. M.

Carbon black per 100 ci rubber 06 Plasticity ui black master batch Log Rof black master batch Log R of complete mix, uneured Vulcanizatn CurcLogs -Jg Torsional hysteresis at 280 F 90 Hudms (Adams) 'remue(lbs/sqm.)

Ultimate elongation l .{331

'Ihe above data show that the improvements in physical propertiescharacteristic oi the invention are retained when the proportion ofcarbon black is increased to amounts substan- 401 tially higher thanthose of ordinary tread stocks.

Stocks containing more than 50% of carbon black on the rubber content,ordinarily too hard for factory processing without the addition of de1eterious amounts of softeners, are, given a normal plasticity andhardness by the process of the invention. 'Ihe lower tensile strengthand abrasion resistance of the 65%-black stocks in the above example aredue largely to an undercured state resulting from the increasedretarding eil'ect of the higher amount of black, and would be remediedby the use of more sulfur and/ or accelerator. Example 5.-A tread stockusing a thiuram type of organic accelerator, namely. tetramethyl thiuramdisulphide, in which the carbon black master batch had been hightemperature milled for 30 minutes at 300 F., when compared with asimilar stock that had been prepared in the usual manner, both stocksbeing cured at 20 pounds per sq. in. steam pressure, gave the followinresults:-

Conven- Cxne in H. T. minutes tgtlld method Log.. of resistivity ofilnal mix.

(uncured) 10. 2 l2 3D 7. 1 l2 Logia oi resistivity of cured stocks 60 6.9 l2 90 6. l2 Torsional hysteresisat 280 F 90 135 .057 30 100 140Abrasion resistance (low speed test). 60 100 125 90 1(1) 123 30 100 127Abrasion resistance (high speed) 60` 100 120 90 100 123 .30 30 44Hardness (Adams) 60 29 40 90 30 30 .off from the scale.

g the pendulum is deilected. For example. a dumbbell test piece ofrubber may be gripped at either end by a stationary upper clamp and alower clamp, the latter being lixed to the hub oi a horizontallydisposed disc or wheel graduated in degrees. A sight is fixed adjacentto the periphery of the disc. The pendulum is set in rotaryV omillationand the amplitudes o1 rotation` read The apparatus is enclosed in aconstant temperature oven having a glass door'or window through whichthe observations may be made. The dimensions oi the rubber test pieceand the weight of the parts suspended from the test piece vshould be so'designed that the rubber is under only a negligible elongation, such asless than 5%. The torsional hysteresis values set forth inthespecification and claims refer in every instance to measurements madewhile the rubber is under negligible elongation. 'Ihe lower the observedvalue of K, the lqwer is the hysteresis or energy loss'. In terms ofservice, this means less heat developed during repeated stresses andvhence there is a tendency toward longer life of vthe rubber tire.Ordinary tread stocks vulcanized by means of sulphur and the usualorganic accelerators, generally give values of Kw ranging from 0.12 to0.30.

The abrasion resistance is expressed by figures which are inverselyproportional to the amount of wear (reduction in thickness) effectedduring a iixed number of cycles on the United States Rubber Companyabrasion testing machine. In the low speed test the machine is operatedw'ith the abrasive wheel rotating at 180 R. P. M. and with a total loadon the sample of 6 lbs., while in the high speed? test the speed is1130R. P. M. and the total load 4 lbs.

The permanent se is determined by measuring the distance bet-Ween benchmarks on a dumbbell tensile test piece one minute after rupture.

In carrying out the invention the usual softeners may be included, ifdesired, in the initial mixture of rubber and black according to commonpractice for the purpose of softening the rubber` 5 and facilitatingtheadmixture and distribution `of the black therein,-for example, suchsofteners as oils, tars, fatty acids, fatty acid soaps, mining out ofthe novel heating and milling process;

in this case, however, care must be taken to ensure that the mixturedoes not become 4scorched or pre-vulcanized to such an extent that itcannot be re-plasticized to permit calendering or ex- 5 truding.Furthermore while sulphur is generally used as the vulcanizing agent,other known vulcanizing agents such as the thiuram polysulfides, e. g.tetramethyl thiuramdis'ulphide, may be used within the broad scope ofthe invention,

and the process may be modiiled to accommodate such materials.

Improved dispersion and resistivity are also obtained whenrubber-and-black mixtures treated according to the invention arevulcanized-to hard 5 rubber (ebonite). For example, mixtures of 100parts of rubber and 45 parts oi' carbon blackone of them treatedconventionally, the other mixed conventionally and then milled for 30minutes at 300 to 340 F. and recovered-were 0 each compounded with 45parts of sulfur and vulcanized for four hours at 298 F. Theresistivities oi' the resulting ebonites were 10"I ohmcentimeters forthe conventional stock, and greater than 1012 ohm-centimeters for the H.T.

l 5 M. stock.

Whereas the invention is adaptable broadly to all kinds of black, it isparticularly concerned with what are known as rubber reinforcing blacks,which blacks are herein distinguishable 0 from the so called soft rubberblacks, which are non-reinforcing and substantially non-fiocculable byheat, and from blacks like paint black and ink black which interferewith the production oi' well cured vulcanizates due to their very' "5pronounced inhibiting effect on vulcanization.

Wherever the term "carbon black occurs, it is to be understood asmeaning a reinforcing rubber black manufactured by any process andl moreparticularly by the partial combustion of natural i0 gas and having arelatively high degree of sub- 1.0 tank linings,` ball mill linings,chute linings, paving blocks, outer sheathing for electrical oonductors,etc.

For example, whereas heretofore tire tread blacks such as channel blackhave generally not 73 been unsable inshoe soling compounds because ofresulting undesired hardness in the uncured and cured stocks, thepresent inventiony provides not only a means for using such a black inplace of the usual soft black, to give a soft, easily calenderablestock, but also provides soling having two to three times the abrasionresistance of the soft-black soling.

'Ihe term rubber is used in its usual generic sense as applicable tocaoutchouc and similar vulcanizable natural gums, as well as to various'synthetic rubbers and rubber-like products which are artificiallyprepared and which have properties in common with natural rubber wherebythey may be adapted to the same commercial uses.

While certain theories and explanations have been advanced in an attemptto explain what is ,thought to be the mechanism of the invention, it

is to be understood that the invention is not to be restricted to or bebound by the same, but is limited solely by the claims wherein it isintended to claim all novelty inherent in the invention as ispermissible in view of the prior art.

Having thus described our invention what we claim and vdesire to protectby Letters Patent is:

1. A method of manufacturing rubber products having unusually highresistance to abrasion when vulcanized which comprises incorporatinguinto rubber a relatively largel amount of a rubber reinforcing blackand mixing to a substantially homogeneous condition, subsequentlyseverely flocculating the black in the rubber mass and masticating themixture to bring about substantially complete particulate dispersion ofthe black throughout the mass without serious degradation of the rubber,completing the incorporation of vulcanizing and other desiredingredients, shaping the mass as desired and vulcanizing the rubber. x

2. A method of manufacturing rubber products having unusually highresistance to abrasion when vulcanized which comprises subjecting ahomogeneous mix comprising unvulcanized rubber and substantial amountsof carbon black to heat at a sufficiently high temperature and for asufficient length of time to cause severe ilocculation of the black inthe rubber and masticating the so heat-treated batch until the specicelectrical resistivity of the mix rises to a value of at least aboutlO12ohm-centimeters without serious degradation of the rubber.

3. A method of manufacturing rubber products having unusually highresistance to abrasion when vulcanized'which comprises incorporatinginto rubber a relatively large amount of a rubber reinforcing black andmixing to a substantially homogeneous condition, subsequently causing asevere flocculation of the black in the rubber mass by subjecting themass to a heat treatment at a temperature at least substantially above250 F. and masticating the mixture to bring about substantially completeparticulate dispersion of the black throughout the mass without seriousdegradation of the rubber; completing incorporation of vulcanizing andother desired ingredients, shaping the mass a desired and vulcanizingthe rubber.

4. A process of producing a vulcanized r'ubber product having anunusually high resistance to abrasion which comprises in addition to theconventional steps of plasticizing and mixing a rubber batch to whichhas been added a relatively large amount of a rubber reinforcing black,the` a smooth,rplastic consistency suitable for the incorporation ofadditional compounding and vulcanizing ingredients without seriousdegradation of the rubber.

5. A process of producing a vulcanized rubber product having anunusually high resistance to' abrasion which comprises in additionto theconventional steps of plasticizing and mixing a rubber batch to whichhas been added a relatively large amount of a rubber reinforcing black,the steps of heating the rubber mix when it is substantiallyhomogeneous, in a, heater at a temperature above 300 F, and then millingthe so heat-treated stock to a smooth, plastic consistency suitable forthe incorporation of additional compounding and vulcanizing ingredientswithout serious` degradation of the rubber.

6. A process of producing a vulcanized rubber product having anunusually high resistance to abrasion which comprises in addition to theconventional steps of plasticizing and mixing a rubber batch to whichhas been added a relatively large amount of a rubber reinforcing black,the

steps of heating the homogeneous rubber mix to a suiciently hightemperature to render -the surface of the mix rough and dull inappearance and milling the so heat-treated stock to a smooth plasticconsistency suitable for the incorporation of additional compounding andvulcanizing ingredients without serious degradation yo1' the rubber.

7. A process of producing a vulcanized rubber product having anunusually high resistance to abrasion which comprises in addition to theconventional steps of plasticizing and mixing a rubber batch to whichhas been added a relatively Ilarge amount of a. rubber reinforcingvblack, the

steps of heating and masticating the homogeneous mix at a suilcientlyhigh temperature and for a sutlicient length of time to produce rst a.decrease in the specific electrical resistivity by a factor on the orderof at least 1000 followed by an increase in the specific electricalresistivity by a factor on the order of at least 1,000,000 withoutserious degradationy of the rubber.

-8. A method of processing a tire tread stock preliminary to the usualshaping and vulcanizing operations which comprises incorporatirg andworking into a rubber composition, a relatively large amount of carbonblack until the rubber mass has attained a smooth, glos:y andhomogeneous appearance, subjecting the homogeneous rubber mix to a heattreatment within a temperature range of from about 300 F. to about 370F. and milling the so heat-treated mass to a smooth, plastic consistencysuitable for the incorporation of compounding ingredients withoutserious degradation of the rubber, and completing the incorporation ofvulcanizing and other desired ingrediens prior to the iinal shaping andvulcanization of the rubber stock.

9. A method of processing a tire tread stock preliminary to the usualshaping and Vulcanizing operations which comprises incorporating andworking into a rubber composition, a relatively large amount of carbonblack until the mass has attained a smooth. glossy and homogeneous apoutserious degradation of the rubber, and com-A pleting incorporation ofvulcanizing and other tallic oxide, vulcanizingand acceleratingingredients, to a heat treatment within a temperature range of fromabout 300 F. to about 370 F. for from 10 to about 60 minutes, andmilling the so heat-treated mass to a smooth plastic consistencysuitableffor the incorporationof additional compounding ingredients, andcompleting the incorporation of vulcanizing and other desiredingredients prior tol the iinal shaping and vulcanization of the rubberstock.

11. As a. new article of manufacture, a rubber product comprising thevulcanization product of a rubber mix comprising rubber, sulphur and atleast 25 parts by weight of a rubber reinforcing black per parts byweight of rubber in which thereinforcing black is in a. substantiallycomplete particulate state of dispersion in the rubber resulting fromseverely flocculating the black while homogeneously mixed in the rubberand masticating the mixture to bring about substantially completedispersion of the black and which vulcanization product has a torsionalhysteresis value not exceeding 0.06 at 280 F.

12. As a new article of. manufacture, a rubber product comprising thevulcanization product of a rubber mix comprisingrubber, sulphur, andv atleast 40 parts by weight of carbon black per 100 parts by weight ofrubber in which the reinforcing black is in a substantially completeparticulate state of dispersion in the rubber resulting from severelyflocculating the black while homogeneously mixed in the rubber andmasticating the mixture to bring about substantially complete dispersionof the black and which vulcanizatin product has a torsional hysteresisvalue of les than 0.08 at 280 F.

13. As a new article of manufacture, a rubber product comprising thevulcanization product of a rubber mix comprising rubber, sulphur, and atleast 40 parts by weight of carbon black per 100 parts by weight of.rubber in which the reinforcing black is in a substantially completeparticulate state of dispersion in the rubber "resulting from severelyflocculatlng the black while homogeneously mixed in the rubber andmasticating the mixture to bring about substantially complete dispersionof the black and which vulcanization product has a torsional hysteresisvalue not exceeding 0.06 at 280 F.

14. As an article of manufacture, a rubber` product comprising thevulcanization product of a rubber mix comprising rubber, sulphunand atleast 25 percent by weight based on the rubber of a rubber reinforcingblack in which the reinforoing black is in a substantially completeparticulate state of dispersion in the rubber resulting from severelyflocculating the black while homogeneously mixed in the rubber andmasticating the mixture to bring about substantially complete dispersionof the black, and which vulcanization product has a torsional hysteresisvalue not exceeding 0.06 at 280 F. and a/speciic electrical resistivityequal to at least 1012 ohmcentimeters.

.15.' As a new article of manufacture, a rubber particulate state o!dispersion in the rubber re-y product comprising the vulcanizationproduct of a rubber mix comprising rubber, sulphur, and at least 40parts by weight of carbon black per 100 parts by weight of rubber inwhich the reinforcing black is in a substantially complete particulatestate of dispersion in the rubber resulting from severely fiocculatingthe black while homogeneously mixed in the rubber and masticating themixture to bring about substantially complete dispersion of the blackand which vulcanization product has a torsional hysteresis value notexceeding 0.06 at 280 F. and a. specic electrical resistivity equal atleast 1012 ohm-centimeters.

trical resistivity of at least 101* ohm-centimeters.

and a torsional hysteresis value of less than 0.06 at 280"4 F.

17. As a new article o1' manufacture a tire having a vulcanized treadportion of improved abrasioncharacteristics comprising at least 40 partsby weight of a rubber reinforcing black per 100 parts by weight ofrubber in which the reinforcing black is in a substantially completesulting from severely occulating the black while homogeneously mixed inthe rubber and masticating the mixture to bring about substantiallycomplete dispersion of the black and which tread portion is' furthercharacterized in having a specific electrical resistivity of at least1012 ohmcentimeters and a torsional hysteresis value of less than 0.06at 280 F. y

18. A sulfur-rubber vulcanizate containing a. relatively largeproportion ofV normally heatocculable carbon black in a highlydeflocculated and particulate state of dispersion resulting from aprocess as set forth in claim 1.

19. A rubberl composition comprising at least 40% by weight of. carbonblack based on the rubber content resulting from the process as setforth in claim 3 and having in both the unvulcanizcd and the vulcanizedstates a` speciiic electrical resistivity equal to at least 1012ohmcentimeters, said carbon black being of a type which in suchproportion in vulcanized rubber normally permits in the vulcanizedcomposition a specic electrical resistivity of not more thanV about 109ohm-centimeters.

20. As a new article of manufacture, a rubber product having anunusually high resistance to abrasion resulting from the process as setforth in claim 5, said product having a torsional Vhysteresis value notexceeding 0.08 at 280 F.

ROSCOE H. GERKE. GEORGE H. GANZHORN. LOUIS H. HOWLAND. HUGH MSMALL'WOOD.

DISCLAIMER y `,1l8,601.-Ro.en:oe H. Gerke, Nutley, George H. Ganzhorn,West Ellilewood, Louis H.

Howland, Nutley, N. J., MANUFACTURE or' RUBBER.

` filed December 13, 1940, by the assignee,rUmIted Hereb enters thisdisclaimer to claim [i-icl Gazette January 21, 1941 and Hugh M.Smallwood,

Patent dated Ma ew York, N. Y. 24, 1938. DisclaimerA tates RubberCompany.

s 4 and 5 o f said patent.

particulate state o! dispersion in the rubber re-y product comprisingthe vulcanization product of a rubber mix comprising rubber, sulphur,and at least 40 parts by weight of carbon black per 100 parts by weightof rubber in which the reinforcing black is in a substantially completeparticulate state of dispersion in the rubber resulting from severelyfiocculating the black while homogeneously mixed in the rubber andmasticating the mixture to bring about substantially complete dispersionof the black and which vulcanization product has a torsional hysteresisvalue not exceeding 0.06 at 280 F. and a. specic electrical resistivityequal at least 1012 ohm-centimeters.

trical resistivity of at least 101* ohm-centimeters.

and a torsional hysteresis value of less than 0.06 at 280"4 F.

17. As a new article o1' manufacture a tire having a vulcanized treadportion of improved abrasioncharacteristics comprising at least 40 partsby weight of a rubber reinforcing black per 100 parts by weight ofrubber in which the reinforcing black is in a substantially completesulting from severely occulating the black while homogeneously mixed inthe rubber and masticating the mixture to bring about substantiallycomplete dispersion of the black and which tread portion is' furthercharacterized in having a specific electrical resistivity of at least1012 ohmcentimeters and a torsional hysteresis value of less than 0.06at 280 F. y

18. A sulfur-rubber vulcanizate containing a. relatively largeproportion ofV normally heatocculable carbon black in a highlydeflocculated and particulate state of dispersion resulting from aprocess as set forth in claim 1.

19. A rubberl composition comprising at least 40% by weight of. carbonblack based on the rubber content resulting from the process as setforth in claim 3 and having in both the unvulcanizcd and the vulcanizedstates a` speciiic electrical resistivity equal to at least 1012ohmcentimeters, said carbon black being of a type which in suchproportion in vulcanized rubber normally permits in the vulcanizedcomposition a specic electrical resistivity of not more thanV about 109ohm-centimeters.

20. As a new article of manufacture, a rubber product having anunusually high resistance to abrasion resulting from the process as setforth in claim 5, said product having a torsional Vhysteresis value notexceeding 0.08 at 280 F.

ROSCOE H. GERKE. GEORGE H. GANZHORN. LOUIS H. HOWLAND. HUGH MSMALL'WOOD.

DISCLAIMER y `,1l8,601.-Ro.en:oe H. Gerke, Nutley, George H. Ganzhorn,West Ellilewood, Louis H.

Howland, Nutley, N. J., MANUFACTURE or' RUBBER.

` filed December 13, 1940, by the assignee,rUmIted Hereb enters thisdisclaimer to claim [i-icl Gazette January 21, 1941 and Hugh M.Smallwood,

Patent dated Ma ew York, N. Y. 24, 1938. DisclaimerA tates RubberCompany.

s 4 and 5 o f said patent.

